HP BL680c XenServer Administrator's Guide 4.1.0 - Page 21

Warning, 2.5. Shared LVM storage over FC or iSCSI hardware HBAs

Page 21 highlights

Storage Shared iSCSI support using the software iSCSI initiator is implemented based on the Linux Volume Manager (LVM) and provides the same performance benefits provided by LVM VDIs in the local disk case. Shared iSCSI SRs using the software-based host initiator are capable of supporting VM agility using XenMotion: VMs can be started on any XenServer Host in a resource pool and migrated between them with no noticeable downtime. The LVM VDIs used in software-based iSCSI SRs VDIs do not provide support for sparse provisioning or fast cloning. iSCSI SRs utilize the entire LUN specified at creation time and may not span more than one LUN. CHAP support is provided for client authentication, during both the data path initialization and the LUN discovery phases. 3.2.4.1. XenServer Host iSCSI configuration All iSCSI initiators and targets must have a unique name to ensure they can be uniquely identified on the network. An initiator has an iSCSI initiator address, and a target has an iSCSI target address. Collectively these are called iSCSI Qualified Names, or IQNs. XenServer Hosts support a single iSCSI initiator which is automatically created and configured with a random IQN during host installation. The single initiator can be used to connect to multiple iSCSI targets concurrently. iSCSI targets commonly provide access control via iSCSI initiator IQN lists, so all iSCSI targets/LUNs to be accessed by a XenServer Host must be configured to allow access by the host's initiator IQN. Similarly, targets/LUNs to be used as shared iSCSI SRs must be configured to allow access by all host IQNs in the resource pool. Note iSCSI targets that do not provide access control will typically default to restricting LUN access to a single initiator to ensure data integrity. If an iSCSI LUN is intended for use as a shared SR across multiple XenServer Hosts in a resource pool ensure that multi-initiator access is enabled for the specified LUN. The XenServer Host IQN value can be adjusted using XenCenter, or via the CLI with the following command when using the iSCSI software initiator: xe host-param-set uuid= other-config:iscsi_iqn= Warning It is imperative that every iSCSI target and initiator have a unique IQN. If a non-unique IQN identifier is used, data corruption and/or denial of LUN access can occur. Warning Do not change the XenServer Host IQN with iSCSI SRs attached. Doing so can result in failures connecting to new targets or existing SRs. 3.2.5. Shared LVM storage over FC or iSCSI hardware HBAs XenServer Hosts support Fibre Channel (FC) storage area networks (SANs) through Emulex or QLogic host bus adapters (HBAs). All FC configuration required to expose a FC LUN to the host must be completed manually, including storage devices, network devices, and the HBA within the XenServer host. Once all FC configuration is complete the HBA will expose a SCSI device backed by the FC LUN to the host. The SCSI device can then be used to access to the FC LUN as if it were a locally attached SCSI device. 15

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Storage
15
Shared iSCSI support using the software iSCSI initiator is implemented based on the Linux Volume Manager
(LVM) and provides the same performance benefits provided by LVM VDIs in the local disk case. Shared
iSCSI SRs using the software-based host initiator are capable of supporting VM agility using XenMotion:
VMs can be started on any XenServer Host in a resource pool and migrated between them with no notice-
able downtime. The LVM VDIs used in software-based iSCSI SRs VDIs do not provide support for sparse
provisioning or fast cloning.
iSCSI SRs utilize the entire LUN specified at creation time and may not span more than one LUN. CHAP
support is provided for client authentication, during both the data path initialization and the LUN discovery
phases.
3.2.4.1. XenServer Host iSCSI configuration
All iSCSI initiators and targets must have a unique name to ensure they can be uniquely identified on the
network. An initiator has an iSCSI initiator address, and a target has an iSCSI target address. Collectively
these are called iSCSI Qualified Names, or IQNs.
XenServer Hosts support a single iSCSI initiator which is automatically created and configured with a ran-
dom IQN during host installation. The single initiator can be used to connect to multiple iSCSI targets con-
currently.
iSCSI targets commonly provide access control via iSCSI initiator IQN lists, so all iSCSI targets/LUNs to
be accessed by a XenServer Host must be configured to allow access by the host's initiator IQN. Similarly,
targets/LUNs to be used as shared iSCSI SRs must be configured to allow access by all host IQNs in the
resource pool.
Note
iSCSI targets that do not provide access control will typically default to restricting LUN access to a
single initiator to ensure data integrity. If an iSCSI LUN is intended for use as a shared SR across
multiple XenServer Hosts in a resource pool ensure that multi-initiator access is enabled for the
specified LUN.
The XenServer Host IQN value can be adjusted using XenCenter, or via the CLI with the following command
when using the iSCSI software initiator:
xe host-param-set uuid=<valid_host_id> other-config:iscsi_iqn=<new_initiator_iqn>
Warning
It is imperative that every iSCSI target and initiator have a unique IQN. If a non-unique IQN identifier
is used, data corruption and/or denial of LUN access can occur.
Warning
Do not change the XenServer Host IQN with iSCSI SRs attached. Doing so can result in failures
connecting to new targets or existing SRs.
3.2.5. Shared LVM storage over FC or iSCSI hardware HBAs
XenServer Hosts support Fibre Channel (FC) storage area networks (SANs) through Emulex or QLogic
host bus adapters (HBAs). All FC configuration required to expose a FC LUN to the host must be completed
manually, including storage devices, network devices, and the HBA within the XenServer host. Once all FC
configuration is complete the HBA will expose a SCSI device backed by the FC LUN to the host. The SCSI
device can then be used to access to the FC LUN as if it were a locally attached SCSI device.